U.S. Pat. No. 7,585,860 discloses a variety of substituted oxazolidinone derivatives and their salts, processes for their preparation, pharmaceutical compositions comprising the derivatives, and methods of use thereof. These compounds are anticoagulants which inhibit the blood coagulation factor Xa with increased selectivity. Among them, Rivaroxaban, 5-chloro-N-[[(5S)-2-oxo-3-[4-(3-oxomorpholin-4-yl)phenyl]oxazolidin-5-yl]methyl]thiophene-2-carboxamide, acts as inhibitor of clotting factor Xa and which is used as agent for the prophylaxis and/or treatment of thromboembolic disorders, in particular myocardial infarction, angina pectoris, reocclusions and restenoses after angioplasty or aortocoronary bypass, stroke, transient ischaemic attacks, peripheral arterial occlusive diseases, pulmonary embolisms or deep venous thromboses. Rivaroxaban is represented by the following structural formula I:

Rivaroxaban is sold by Bayer under the brand name Xarelto® and it is orally administered as tablets containing 10 mg of Rivaroxaban.
Various processes for the preparation of Rivaroxaban and its intermediates are apparently disclosed in U.S. Pat. Nos. 7,585,860; 7,351,823 and 7,816,355; PCT Publication Nos. WO 2011/012321, WO 2011/080341, WO 2011/098501, WO 2012/032533, WO 2012/156983, WO 2013/027225, WO 2013/046211, WO 2013/105100, WO 2013/118130 and WO 2013/164833; and J. Med. Chem. 2005, 48, 5900-5908.
According to U.S. Pat. No. 7,585,860 (hereinafter referred to as the U.S. '860 patent), Rivaroxaban is prepared by reacting 4-[4-[(5S)-5-(aminomethyl)-2-oxo-1,3-oxazolidin-3-yl]phenyl]morpholine-3-one of formula (II) with thiophene carboxylic acid of the formula (III) or else with a corresponding carbonyl halide, or else with a corresponding symmetric or mixed carboxylic anhydride of the carboxylic acid of the formula (III) in an inert solvent, if appropriate in the presence of an activating or coupling agent and/or a base. As per the process exemplified in example 44 of the '860 patent, Rivaroxaban is prepared by drop-wise addition of 5-chlorothiophene-2-carbonyl chloride to a solution of 4-[4-[(5S)-5-(aminomethyl)-2-oxo-1,3-oxazolidin-3-yl]phenyl]morpholine-3-one in pyridine at 0° C. under argon, followed by removal of ice-cooling and stirring the reaction mixture at room temperature for 1 hour and then admixing with water. After addition of dichloromethane and phase separation, the aqueous phase was extracted with dichloromethane. The combined organic phases were dried, filtered, and evaporated in vacuo. The residue was purified by Flash chromatography (dichloromethane/methanol mixtures) to produce Rivaroxaban.
According to the PCT Publication No. WO 2013/164833 (hereinafter referred to as the WO '833 publication), Rivaroxaban is prepared by reacting 5-Chlorothiophene-2-carboxylic acid with a sulfonylating agent (e.g., methanesulfonyl chloride or p-toluenesulfonyl chloride) in the presence of a base such as 1-Methylimidazole in dichloromethane to produce a reaction mass containing a corresponding sulfonyl ester intermediate, followed by condensation with (S)-4-[4-[5-(Aminomethyl)-2-oxo-oxazolidin-3-yl]phenyl]morpholin-3-one to produce Rivaroxaban.
Rivaroxaban is known to exhibit polymorphism and various solid state forms including crystalline modifications (I, II & III), amorphous form, hydrate form, dihydrate form, solvated forms and co-crystals of rivaroxaban are apparently disclosed in U.S. Pat. No. 8,188,270; and PCT Publication Nos. WO 2009/149851, WO 2010/075631 and WO 2012/004245.
U.S. Pat. No. 8,188,270 (hereinafter referred to as the U.S. '270 patent), assigned to Bayer Schering Pharma, discloses three crystalline modifications (modifications I, II & III) and four solid state forms (an amorphous form, a hydrate, an NMP solvate and an inclusion compound with THF) of Rivaroxaban, processes for their preparation, and characterizes the modifications and the solid state forms by powder X-ray diffraction (XRPD), Infra Red spectrum (IR), Raman spectrum, Far Infra Red spectrum (FIR), Near Infra Red spectrum (NIR) and Differential Scanning Calorimetric thermogram (DSC).
The U.S. '270 patent teaches that when Rivaroxaban was originally produced, for example, as per the process described in the U.S. '860 patent, the crystal form was crystal modification I (hereinafter referred to as the Crystalline Form I), which is characterized by having melting point of 230° C.; a powder X-ray diffraction spectrum having peaks expressed as 2-theta angle positions at 8.9, 12.0, 14.3, 16.5, 17.4, 18.1, 19.5, 19.9, 21.7, 22.5, 23.4, 24.1, 24.5, 24.7, 25.6, 26.4, 26.7, 30.0, 30.1 and 31.8 degrees; and an IR spectrum having bands at 564, 686, 708, 746, 757, 830, 846, 920, 991, 1011, 1056, 1077, 1120, 1146, 1163, 1219, 1286, 1307, 1323, 1341, 1374, 1411, 1429, 1470, 1486, 1517, 1546, 1605, 1646, 1669, 1737, 2867, 2895, 2936, 2976 and 3354 cm−1.
The U.S. '270 patent neither discloses nor teaches any processes (except the process described in the U.S. '860 patent) for the preparation of crystal Modification I of Rivaroxaban. However, the processes for preparation of the crystal Modification I of Rivaroxaban as described in the aforementioned prior art suffer from several disadvantages such as lack of reproducibility; contamination of the desired crystal Modification I with other solid state forms and solvated forms; require the use of column chromatographic purifications; the use of excess amounts of solvents which generate a large quantity of chemical waste which is difficult to treat. The main drawback of the processes for the preparation of Rivaroxaban as described in the U.S. '860 patent is that the crystal Modification I of Rivaroxaban obtained by the process described therein does not have satisfactory purity (e.g., about 92% purity by HPLC) and which is found to be contaminated with other polymorphic forms and solvated forms.
Based on the aforementioned drawbacks, the crystal Modification I of Rivaroxaban obtained according to the prior art processes is an impure form and therefore not suitable for pharmaceutical formulations and therapeutic use thereof.
A need still remains for simple, cost effective, consistently reproducible and environmentally friendly processes for preparing highly pure crystal Modification I of Rivaroxaban which is free from other polymorphs and solvated forms.